--> Skip to main content

Exposure Reciprocity



There are two competing variables in making a properly exposed negative (actually three I guess if you count film speed.) But if you're just getting started with film photography you may have heard of reciprocity as it pertains to exposure.

By the way reciprocity should not be mistaken for a shortening of reciprocity failure as I often hear people mis-speak.

Reciprocity is the relationship between the length of time of an exposure and the light coming in through the lens controlled by the aperture. In theory, (and usually in practice) doubling the time of an exposure and halfing the light coming in will result the exact same density negative or transparency.

For example, if you meter (or using the "Sunny 16" rule) an exposure as say f16 at 1/125th, your negs would be exposed* exactly the same as if you used:


f32 @ 1/30th
f22 @ 1/60th
f16 @ 1/125th
f11 @ 1/250th
f8 @ 1/500th
f5.6 @ 1/1000th

Note I said exposed exactly the same, not look exactly the same. Though the density of your photo should look exactly the same, the smaller apertures will result in greater depth of field (objects closer and further from the area where you focused will remain in focus.) With a larger aperture the depth of field is shallower (the area near and far from the area where you focused appears less in focus.)

Another thing for photo newbies to note: the way aperture values are marked is somewhat counter intuitive. As the aperture size increases, the number gets smaller. Lenses are usually described by their focal length and their maximum aperture. So a standard old-skool lens for 35mm film is the 50mm lens, and probably the most common maximum aperture is f2. What the f2 is describing is when the aperture is all the way open, the hole measures half of the focal length: 1/2 of 50mm = 25mm.  As you click down the scale on a 50mm lens, the aperture (the size of the hole of the iris) measures:

f2 (1/2 of 50mm) = 25mm
f2.8 (1/2.8 of 50mm) = 17.85mm
f4 (1/4 of 50mm) = 12.5mm
f5.6 (1/5.6 of 50mm) = 8.93mm
f8 (1/8 of 50mm) = 6.25mm
f11 (1/11 of 50mm) = 4.55mm
f16 (1/16 of 50mm) = 3.125mm

Not to say that you remembering any of those numbers is important, but it might be helpful to understand. Especially why a number that goes up means more.

Got it?

Comments

Popular posts from this blog

Linhof Serial Year List - Salomon Says

Recently I've acquired a few Linhof cameras. I got a 5x7 view camera from Oakland Museum's White Elephant Sale. Later I stumbled upon a Color Kardan 90 Jahre Jubalaeum edition on Craigslist. And more recently, I found a "baby Technika" 2x3 (6x9) at Oakland's East Bay Depot for Creative Re-use. Not knowing much about Linhof large format cameras, I tried getting more info online, and came across a strange thread on the Large Format Photography Forum . Basically on this thread various Linhof owners ask a guy named Bob Salomon what year their Linhof was made. And the thread is over 100 pages long! Sifting through that thread is mindnumbing. Why Bob doesn't just publish the list of serial numbers is beyond me. Maybe it's just nice to feel needed. So I started compiling a spreadsheet of the serial numbers and the answer Bob gives. If you don't feel like spending a couple days reading this thread to get a hint as to the age of your Lin

Lossy DNG File Sizes by ISO.

Fairly recently I discovered the magic of lossy DNG's. My stock photo library is ever growing. Though JPG's might really be enough for my archive, I've been keeping my raw files. RAW files take up lots of space. And RAW files can't typically keep user generated EXIF data in the file. RAW files keep their keywords and other metadata in a sidecar, that is if you regularly save the EXIF data to file. So recently I've been converting all my RAW files to lossy DNG's. After testing the highest ISO setting on the new-to-me A7R IV, I converted the files to lossy DNG's only to find a surprise. The very high ISO lossy DNG's were much larger than the original Sony RAW files! Lossy ARW vs Lossy DNG full image sample So I thought it would be a good test to shoot from the lowest to highest ISO, convert to lossy DNG and see where the file size savings invert. Here's the data as seen in the above screen shot: ISO Lossy Sony ARW Raw file size (MB) Lossy DNG file siz

From the Archive: Obsolete Film Data Sheet Scans - ORWO Information

Here's a sheet I got from writing ORWO Technischer Kundendienst back in the 1980's. It lists development times for all the ORWO Black and White films sold for export at the time (NP15, NP22, NP 27) combined with western developers Microphen, Atomal, Rodinal, Refinal, D-76, & ID-11. A little bit of ORWO history- Germany's big photo film/paper manufacturer up until Germany's losing WWII was AGFA (short for  A ktien G esellschaft F ür A nilinfabrikation - or corporation for some sort of plastic manufacture.) Germany was occupied by the winning powers USSR/USA/GB/FR and the rift between the USSR led to some complications for industries. Depending on your view of history the US and western allies were much friendlier to the land they occupied (remember the USSR lost many millions of their citizens to the NAZIs which made them much less tolerant.) In any case, some factories in the east moved to the west with many key employees. Most photo enthusiasts know of the t